20 ER Diagram Interview Questions and Answers

An Entity Relationship Diagram (ERD) is a graphical representation of the relationships between entities in a database. These diagrams are used by database developers to map out the structure of a database and visualize how the different entities relate to each other. If you are applying for a position that involves database development, you will likely be asked questions about ERDs during your interview. In this article, we review some of the most common ERD interview questions and provide tips on how to answer them.

ER Diagram Interview Questions and Answers

Here are 20 commonly asked ER Diagram interview questions and answers to prepare you for your interview:

1. What is an ER Diagram?

An ER diagram is a graphical representation of an entity relationship model. It is used to represent the relationships between entities in a database.

2. Can you explain the different symbols used in an ER diagram?

The three most common symbols used in an ER diagram are rectangles, diamonds, and ovals. Rectangles are used to represent entities, while diamonds represent relationships between those entities. Ovals are used to represent attributes.

3. How do you represent weak entities in ER diagrams?

Weak entities are represented by double rectangles in ER diagrams.

4. What are some of the best practices for designing an ERD?

Some of the best practices for designing an ERD include using a consistent notation, keeping the diagram simple and easy to understand, and using primary and foreign keys to connect related entities.

5. Why are composite keys important when modeling databases with entity-relationship diagrams?

Composite keys are important when modeling databases with entity-relationship diagrams because they can help to uniquely identify each row in a table. This is especially important when modeling databases that will be used for transactional purposes, such as online stores. By using a composite key, you can ensure that each row in the database is uniquely identified, which can help to prevent errors during transactions.

6. What is the difference between a crow’s foot and Chen notation? Which one would you recommend based on your experience using them?

The main difference between crow’s foot and Chen notation is that crow’s foot notation uses boxes to represent entities, while Chen notation uses circles. I would recommend using crow’s foot notation because it is generally easier to understand.

7. In what situations should we use ER diagrams vs UML class diagrams?

ER diagrams are used to model the data stored in a database, while UML class diagrams are used to model the structure of a system. If you are trying to model the relationships between the data in a database, then you would use an ER diagram. If you are trying to model the relationships between the different components of a system, then you would use a UML class diagram.

8. How can cardinality be applied to relationships in ER diagrams?

Cardinality is a way of representing the minimum and maximum number of occurrences of an entity in a relationship. For example, if you have a relationship between two entities, A and B, and you want to indicate that A can be related to B multiple times, you would use a cardinality of 1:N.

9. Is it possible to define inheritance hierarchies with ER diagrams?

Yes, it is possible to define inheritance hierarchies using ER diagrams. This is typically done by using a supertype/subtype relationship, where the supertype is the parent class in the inheritance hierarchy and the subtype is the child class.

10. What is normalization?

Normalization is the process of organizing data in a database so that it meets certain requirements, in order to reduce data redundancy and improve data integrity.

11. What is the purpose of creating multiple subtypes or supertypes in an ER diagram?

The purpose of creating multiple subtypes or supertypes in an ER diagram is to provide a more granular level of detail when modeling a specific entity type. This can be useful when trying to track different types of information for a given entity, or when trying to create a more general model that can be applied to multiple entity types.

12. What does it mean to generalize/specialize an object in an ER diagram?

Generalization is the process of creating a more general object from a more specific object. In an ER diagram, this is represented by an arrow going from the more specific object to the more general object. Specialization is the process of creating a more specific object from a more general object. In an ER diagram, this is represented by an arrow going from the more general object to the more specific object.

13. When should I use optionality and why?

Optionality is used to indicate whether an attribute is required or optional. If an attribute is required, then it must be included in every instance of the entity. If an attribute is optional, then it does not have to be included. Optionality is important because it can help to ensure that data is consistent and complete.

14. What is an identifying relationship?

An identifying relationship is a relationship in which the primary key of the parent table is also a foreign key in the child table. This means that the child table cannot exist without the parent table, and the child table cannot be linked to more than one parent table.

15. What do you understand about aggregation, composition, and association?

Aggregation is a relationship between two classes where one class is a part of the other. Composition is a relationship between two classes where one class contains the other. Association is a relationship between two classes where one class is related to the other.

16. What is an attribute? How is it represented in an ER diagram?

An attribute is a characteristic of an entity. In an ER diagram, attributes are represented by oval shapes with the name of the attribute written inside.

17. What is a primary key? How is it represented in an ER diagram?

A primary key is a unique identifier for a given entity. In an ER diagram, it is represented by a bolded, underlined attribute.

18. What is a foreign key? How is it represented in an ER diagram?

A foreign key is a column in a database table that is used to store a reference to the primary key of another table. In an ER diagram, a foreign key is represented by a dashed line that connects the two tables.

19. What is the purpose of data tables that contain only one-to-one relationships?

Data tables that contain only one-to-one relationships are typically used to store data that is not essential to the functioning of the database, but which may be useful for reference purposes. For example, a database for a library might have a table containing information on the authors of the books in the library’s collection. This data would not be essential to the functioning of the database, but it could be useful for reference purposes.

20. What is a recursive relationship?

A recursive relationship is one in which an entity is related to itself. For example, a self-employed person is both an employee and a employer.